1. Field of the Invention
The present invention relates generally to a semiconductor treatment apparatus, and more particularly to an apparatus for recovering impurities on the surface of a semiconductor substrate.
2. Description of the Related Art
It is well known that an impurity such as Na (sodium), K (potassium) or Fe (iron) included in a thin film thermal oxide film formed on a semiconductor substrate adversely affects the electrical characteristics of a semiconductor device, even if the amount of the impurity is very small. Thus, the electrical characteristics of the semiconductor substrate can be enhanced by preventing the impurity from being mixed in the substrate as much as possible.
As conventional methods of analyzing impurities over the surface of the semiconductor substrate, there are known secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), and activation analysis. These methods, however, require expensive apparatuses, and special skill is indispensable in operating such apparatuses. While these methods employ electron beams or light beams and allow local analysis, the evaluation of contamination over the entire surface of the semiconductor substrate cannot be achieved. Thus, the conventional methods are unsuitable for easy analysis of contamination of the entire surface of the substrate. Recently, as methods of analyzing the entire surface of the substrate, two methods have been proposed.
According to a first method or a gas-phase decomposing method, an appropriate thermal oxide film is formed over the surface of a substrate, and the substrate is exposed to vapor of fluoride solution. The oxide film, dissolved by the vapor of fluoride solution, is recovered, in the form of fluoride solution, along with impurities contained in the oxide film. Thus, the impurities contained in the recovered fluoride solution are analyzed by an analyzing apparatus.
According to a second method, a semiconductor substrate, which has not been subjected to a thermal oxidation treatment, is immersed in fluoride solution, and a spontaneous oxide film formed on the surface of the substrate is dissolved. The types and concentrations of impurities contained in the spontaneous oxide film are examined by analyzing the fluoride solution.
The first method, however, includes a thermal oxidation process. Thus, there is a concern that an impurity may be mixed in the formed thermal oxide film from the atmosphere employed in the thermal oxidation process, impurities over the surface of the substrate may be evaporated, or impurities may be diffused from the inner region of the substrate to the surface region of the substrate. In the second method, the amount of fluoride solution necessary for recovering the impurities is excessively greater than that necessary for analyzing the impurities. Thus, the concentration of impurities in the recovered solution is too low to obtain precise analysis data, and impurities in a spontaneous oxide film formed on the lower surface of the substrate, which is not related to impurity analysis, are mixed in the fluoride solution.